1. Field of the Invention
The present invention relates to integrated circuit processing and more particularly to an apparatus and method for recovering spent solvent during the manufacture of electronic circuits and components. The invention further relates to a method of recovering spent solvent from wafer processing apparatus during the manufacture of electronic circuits or components.
2. Related Technical Art
During the manufacture of advanced integrated circuits or circuit elements, it is generally necessary to move substrates and assemblies through a series of different processing steps or stages. This is typically handled by a series of two or more machines known as "steppers" or wafer "tracks" which transport integrated circuit substrates and associated devices along predefined processing paths for implementation of various manufacturing steps.
In manufacturing integrated circuits and other miniaturized components, one or more layers of material such as spin on polymer, photo resist, or similar materials are used in the formation of device features, conductive lines, or intermediate dielectric or protective layers. Such materials are typically deposited in a liquid form containing solvents which allow the materials to flow freely across a given substrate or device surface, especially in spin-on processing techniques. During remaining processing or manufacturing steps, the solvent is extracted or removed and the liquid material forms into a solidified layer. If the solvent is removed at a substantially steady or uniform rate, the resulting upper surface of the deposited material is generally very planar.
Planar surfaces play a key role in the design and manufacture of many advanced electronic circuits, elements, or components. It is necessary to minimize surface variations as much as possible to decrease the effects of parasitics, stray capacitances, and complications due to material stress. In advanced integrated circuit designs it is typically desirable to achieve a surface planarity within 50-200 .ANG. or less. However, problems arise in achieving this goal due to current solvent extraction techniques employed in circuit manufacturing.
Variations in solvent evaporation and removal produce significant thickness and planarity variations in the resulting hardened material surfaces. Therefore, the general atmospheric pressure and any air flow patterns, as well as solvent or chemical concentrations, must be highly controlled during manufacturing steps to satisfy design criteria. Sudden changes in the solvent removal environment result in substantial surface variations. This includes not only the general atmospheric pressure within a processing chamber or station but the atmospheric concentration of evaporated solvent which affects subsequent solvent extraction rates. Since solvent atmospheric concentration changes as a function of the amount of removed solvent, spent solvent must be collected within a processing chamber and removed to maintain a consistent extraction rate. In addition, if the solvent vapor is not removed rapidly enough the suspended solvent can form droplets which fall on the devices being manufactured and cause damage or contamination. This is also true for suspended resist and other materials. Solvent removal is typically accomplished by drawing air from the processing area, or volume, through a manifold which has a reservoir operating under negative pressure where the solvent is separated and deposited. The air, once cleaned of solvent, is then exhausted. However, the solvent accumulates in the reservoir and must be periodically emptied. Therefore, the manufacturing process is typically stopped and spent solvent is removed before further processing occurs in order to maintain the desired planarity and other circuit characteristics.
However, stopping the manufacturing process for solvent removal presents at least two major problems. One problem is an increase in personnel safety problems and contamination due to the probabilities of a solvent spill. At the same time, the processing equipment, area, or plant can become contaminated which decreases production and increases operating costs. A second problem is a decrease in throughput during periodic stoppages and a related difficulty in maintaining adequate control over processing step parameters.
An alternative to reduce these problems is to provide very large solvent reservoirs. However, this increases equipment costs and complexity and requires large exhaust systems. In addition, this only represents a partial mitigation but not a resolution of the problem.
What is needed is a method and apparatus for removing spent solvent while the manufacturing process continues and which decreases the impact of solvent removal activities on the processing and increases manufacturing throughput.